Geomagnetic secular variation in Brazil revealed from archeological materials and lacustrine sediments

English Abstract:

The Southern Hemisphere remains poorly covered by paleo- and archeomagnetic data over the Holocene. This scarcity in field data, when compared with Northern Hemisphere, is critical to better understand the geomagnetic field variations. Two morphological features of the field are severely penalized by the unbalance of data and distribution between two hemispheres. The first feature is the continuous decrease of the dipole moment over the past few centuries. The second is the presence of the lowest total field intensities in South Atlantic, the South Atlantic Magnetic Anomaly (SAMA), which seems to be driven by the strong non-dipole field components. In both cases, any scarcity, quality and resolution of the paleo- and archeomagnetic data are the crucial factors to understand decadal to millennial geomagnetic field oscillations. Here, we discuss the geomagnetic field variations from the previous high-quality archeointensity data from Northeast, Southeast and South Brazil and compare with new lacustrine sediment data. These latter comprise directional data (inclination) obtained from three lacustrine cores sampled in South Brazil whose ages cover the past six millennia. Intensity and inclination results describe the geomagnetic field in both Brazilian regions, accompanying for some periods the geomagnetic field models. However, more data from Southern Hemisphere are needed to improve our understanding about secular variations features at the millennial timescales.